What is the actual amount of energy for %100 of my pack? I'm not just asking here first: I've been trying to find out/understand.

It's seems such a simple question to ask and I can't quite get a straight answer/understanding.

I have an 2s8p Eve280 battery arrangement = 560A @24v nominal

I have my BMS set LVD 2.5v/cell 20v/pack to HVD 3.65v/cell 30v/pack
I have my charge equipment set for 28.2v bulk and 27v float.
My Multiplus cuts off at 23v

I know the first <%5 and last >%15 of the discharge curve is pretty useless, and I also am trying to keep DOD to <%80

My BMS and BVM712 shunt do not agree on what percentage the battery is at, and I understand that's because I'm telling them different voltage ranges as well as the fact that most of the usable voltage comes out at 3.3XXv and not over the entire voltage range.

But what is an eve280 and/or 8s eve280 voltage for %0? and %100?

As far as my BMS is concerned it's 20v-29.2v
My Multiplus thinks that it's 23-28.2
And I"m not sure about what my shunt thinks, because I never get to check the VenusPi screen before the power goes off (yes, yes, I know. I'm putting it on it's on PS today. I just haven't had time to do that, yet).

Although, I'm not sure why the BVM display lost power today: the BMS didn't LVD????

1) Your calculations are off. Nominal for 24V-LFP is 25.6V (3.200x8 paralleled cells are irrelevant)
2) Coulomb Counting requires a full cycle before it can do the counting. Depending on what you are using some are more programmable than others with regards to setting parameters & values.
3) Your BMS setting WILL cause trips ! You are literally allowing "to the edge" limits and sure enough, a runner will make itself known. An aggressive Charge profile is not good for LFP.

2.500-2.900 & 3.500-3.650 only represents about 5% of Gross Capacity. A+ Working Voltage Range is 2.900-3.475. A Range is 3.000-3.400.
A+ Cells will always test with More "Actual" capacity than labelled, so a 280AH cells is usually 290AH to 295AH is quite normal. A will just make the spec and Bulk, well you get what you get.

I believe that with the Victron, once you KNOW you have attained your designated 100%, you can set it then as "full" and then the coulomb counting will start as it discharges. There are variations with the softwares & models over the years.

TRY these settings for your Charge Profile, they WORK !
All equipment MUST BE Voltage Corrected & Calibrated (VERY IMPORTANT) see link in my signature on how to do it.
Divide Values X2 for 12V. Multiply X2 for 48V.
Absorb: 28.2 for 15 minutes (3.525vpc) (some call this boost)
Equalize: OFF
Float 27.9V (3.4875vpc)
MIn Volts: 22.0 (2.750vpc)
Max Volts: 28.7 (3.5875vpc)
Rebulk Voltage: 27.7 (3.4625vpc)
End Amps: 14A (*1)

(*1): End Amps is calculated from the Highest AH Battery Pack in a Bank. IE: 200AH X 0.05 = 10A 280AH X 0.05 = 14A.
NB: Victron Forum discussion says EndAmps = TailCurrent
This get's the bank charged to full with high amps (Constant Current) and then float (Constant Voltage) tops off so the cells are on average between 3.475-3.500. I am running 7/24/365 so float is used up by the Inverter + provides whatever the packs will take to top off.

** Coulumbic Efficiency for LFP is 99%

So, in short:
if my equipment is calibrated properly then I can do a full charge, and a full discharge, and trust the reading on my BVM712 shunt to tell me the total extracted power, right? That will tell me what I'm extracting from the pack, that's the "part". How do I get the "whole" %100 (where % = part/whole)

interestingfellow said:

How do I get the "whole" %100 (where % = part/whole)

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I am not concerned with getting the whole 100 percent from my pack. I am more concerned with using only 90 percent and getting a long life from my pack. What is your use case?

Ampster said:

I am not concerned with getting the whole 100 percent from my pack. I am more concerned with using only 90 percent and getting a long life from my pack. What is your use case?

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Oh, no, we agree.

I want to use only %80 of my pack.
But I'm not sure what %100 actually is in order to calculate what %80 is.

And I know that I have my equipment set up in such a way that I am not using %100 or even %80 total capacity.

That's what I'm trying to figure out: if I'm willing to use %80 of the 560ah pack, that's 448ah. I'm trying to figure out what the actual voltage range should be in order to get that 448ah. I know it's somewhere near 2.8v/cell on the low end and 3.5v on the high end, but I don't want to guess and shorten the life on my pack/etc.

Right now I feel like my LVD and HVD are safe, as well as the usable voltage range set up in my equipemnt but iF the way I have my equipment set up means I'm only using 400ah (%71) then I want to get those extra 48ah (%9) to hit %80 DOD. I feel like %80 DOD is super conservative already, so I don't want to leave usable amps in the battery if I need them.
I do need to do a capacity test through my shunt, just to see what it thinks I'm using and go from there, I guess.

interestingfellow said:

I'm trying to figure out what the actual voltage range should be in order to get that 448a

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Try a range of 3.0 to 3.4 volts. it might be more than 80% or slightly less. Do you need exactly 448 Ahr every day?

interestingfellow said:

I want to use only %80 of my pack.

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Do you want to use the top 80% or the bottom or shave 10% off the top and 10% off the bottom?

I suggest you fill your battery fullish so the bms can maintain balance.
Any charge voltage at or above ~27.4 will get your battery full.
I suggest 28 volts to get your battery fuller quicker, thus minimizing the charging stress.
Then run a discharge test at a current representative of your use case to see where first cell starts to nose dive.
Record the pack voltage at which that cell jumps off the cliff.
That is where your inverter low voltage disconnect should be set.
That will give you good capacity while avoiding the stress of drawing the pack too low.
Charge rate is important too.
Typically for LFP cells .5c is the max, .2-.33c are considered optimal.

tl;dr 80% is hard to achieve and you can do better for you battery anyways.

Ampster said:

Try a range of 3.0 to 3.4 volts. it might be more than 80% or slightly less. Do you need exactly 448 Ahr every day?

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Not every day, but I'm learning and refining.

I've never worked with PV before but have been learning for the last 6 months. I purchased a 27' camper 6 months ago and started working on it. I have been living in it for 9 days now, completely off grid. I have a lot left to learn! LOL!

But, i've ran out of power twice because of lack of sun. I know I need a small genny for suppliment as needed, but if I'm loosing and or had an extra %10/50ah, that would be significant.

smoothJoey said:

Do you want to use the top 80% or the bottom or shave 10% off the top and 10% off the bottom?

I suggest you fill your battery fullish so the bms can maintain balance.
Any charge voltage at or above ~27.4 will get your battery full.
I suggest 28 volts to get your battery fuller quicker, thus minimizing the charging stress.
Then run a discharge test at a current representative of your use case to see where first cell starts to nose dive.
Record the pack voltage at which that cell jumps off the cliff.
That is where your inverter low voltage disconnect should be set.
That will give you good capacity while avoiding the stress of drawing the pack too low.
Charge rate is important too.
Typically for LFP cells .5c is the max, .2-.33c are considered optimal.

Click to expand...

I want my pack to be healthy. That being said, probably %10 from the top and the bottom. Running lithium too high or too low will shorten lifespan more than almost anything else that isn't immediately catastrophic, SFAIK.
The inverter side of my Multiplus thinks that it's 28.2-23v. I'll adjust my bottom number according to my discharge test. I do have my multipluss and my Triron's set to boost/bulk at 28.2 and float at 27v, 50a (.09c) max charge from the multiplus when on shore power just because that's low enough without stressing whatever AC source I'm plugged into, and my solar array at %100 will only do 80amps anyway.

Thank you, y'all! BTW keep it coming, I do appreciate it

smoothJoey said:

tl;dr 80% is hard to achieve and you can do better for you battery anyways.

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I don't understand. Better for me by getting more than %80 out?

interestingfellow said:

I want my pack to be healthy. That being said, probably %10 from the top and the bottom. Running lithium too high or too low will shorten lifespan more than almost anything else that isn't immediately catastrophic, SFAIK.
The inverter side of my Multiplus thinks that it's 28.2-23v.

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28.2 volts is good for bulk/absorb.
Are you terminating the charge on tail current or an absorb timer or other?
23 is pretty low.
From your discharge test I suspect you will find somewhere between 24 and 25 volts is better.

interestingfellow said:

I'll adjust my bottom number according to my discharge test. I do have my multipluss and my Triron's set to boost/bulk at 28.2 and float at 27v, 50a (.09c) max charge from the multiplus when on shore power just because that's low enough without stressing whatever AC source I'm plugged into, and my solar array at %100 will only do 80amps anyway.

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I suggest a float voltage of 26.8.

interestingfellow said:

I don't understand. Better for me by getting more than %80 out?

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Please forget the 80% target, its nebulous.
You need to charge into the high knee so that the bms can maintain pack balance.
Its causes a bit stress but its a necessary stress for the greater good.

Going into the low knee is an avoidable stressor.

I can't add anything that hasn't already been said. Looks like solid advice. I will add that I use the bmv-700, and I cannot think of any reason that it would lose power considering the situation. The only time mine ever shuts down is when the battery is removed or otherwise disconnected. I've had only one LVD, and that was the only time my BMV shut down since I installed my pack. I would only ask, to be sure, that you did install the shunt properly on the negative lead? I only ask, because I erroneously installed mine on the POS, initially, even though I knew better:/ Now, I'm not familiar with the VenusPi. Are you saying the Pi loses power, or the whole system looses power? Also, is the Pi on it's own shunt, or does it share a shunt with the BMV? I assume bvm is a typo for BMV? I suspect the interaction between the Pi and the BMV might be creating issues? But I say that with you understanding that it's the only part of your system that I am unfamiliar with.

smoothJoey said:

Are you terminating the charge on tail current or an absorb timer or other?


I suggest a float voltage of 26.8.

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I'm not sure about how tail current and absorption actually work/compare to bulk/float, but on the victron, I have absorption set to 2hrs
I am not sure what I have my Triron's set to, but they have not been getting me to float, anyway, so I have not been worried about absorbtion in them, even though I'm not sure which setting it is in the solar station software. There is an "equalization" in the triron, but I believe that is for desulfating lead acid

smoothJoey said:

Please forget the 80% target, its nebulous.
You need to charge into the high knee so that the bms can maintain pack balance.
Its causes a bit stress but its a necessary stress for the greater good.

Going into the low knee is an avoidable stressor.

General LiFePO4 (LFP) Voltage to SOC charts/tables 12/24/48V

I've looked at several places for a simple, easy to read at a glance "chart document" for LFP. I could not find anything comprehensive. I discovered an XLS Worksheet in my stored file and took parts of that to create this chart, I did not...

diysolarforum.com

How charging works in the context of LFP batteries

How charging works in the context of LFP batteries

diysolarforum.com

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I do have my daly balance set to start balancing at 3.4v and 0.002v difference, if that is important.

I will check those links out, thanks!

Yurtdweller said:

... I erroneously installed mine on the POS, initially, even though I knew better:/

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Nope, right off the 'BMS out' to the rest of the system, but thank you for the suggestion. I'm not sure about why the BVM cut out, but I'm going to figure it out. Thanks!

interestingfellow said:

I'm not sure about how tail current and absorption actually work/compare to bulk/float, but on the victron, I have absorption set to 2hrs
I am not sure what I have my Triron's set to, but they have not been getting me to float, anyway, so I have not been worried about absorbtion in them, even though I'm not sure which setting it is in the solar station software. There is an "equalization" in the triron, but I believe that is for desulfating lead acid

Click to expand...

The second document I linked describes charge termination and why its relevant.
You definitely don't want "equalization" enabled for LFP batteries.

Aiming for 80% maximum is great. If you need the power I would not hesitate to go 100%.
If using greater than 50% on a daily basis I would consider adding a second battery. I don't want to be constantly on the edge.

interestingfellow said:

I do have my daly balance set to start balancing at 3.4v and 0.002v difference, if that is important.

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You want balancing to only occur during charging and only above float level.

time2roll said:

Aiming for 80% maximum is great. If you need the power I would not hesitate to go 100%.
If using greater than 50% on a daily basis I would consider adding a second battery. I don't want to be constantly on the edge.

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It's all about economics. I am getting a divorce and spent what I had on what I could. I am full time boodocking/drydocking with a 27' Jayco that I remodeled the bedroom in and converted the bunkhouse to a work room, new roof, 2100wh panels on top, 14kwh eve280's for the battery, victron stuff, epever stuff, and a ton of nickles and dimes in bits and pieces...

I would have done a larger battery, but I thought this would be good to start with and still do: I just have to learn more about what they will do and also adjust how I do what I do. You don't realize how little 40gal of water is until that is *all the water you have* lol.

I'm counting every dollar, BTU, Wh, lb, ounce, garbage....LOL! It's a trip, I tell ya!

smoothJoey said:

You want balancing to only occur during charging and only above float level.

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Aye. The daly knows if it's charging and 3.4*8=27.2v (my float voltage)(which I may have mistakenly stated as 27.0v earlier). Is something there not correct/adequate?
Also, I meant to ask why you suggested 26.8v float instead of 27.2